Although the present invention is quite well adapted to reciprocating pumps other than mud pumps for circulating drilling mud within a well being drilled, for purposes of simplicity, the invention is discussed particularly as it relates to pistons for mud pumps.
Piston and cylinders for mud pumps are susceptible to a high degree of wear during use because the drilling mud being pumped contains a suspension of particulate, such as drill cuttings, that can be quite erosive. Moreover, mud pumps typically operate at high pressures due to the necessity for pumping the drilling mud through perhaps several thousand feet of drill stem where it emerges at relatively high velocity at the drill bit in order to provide lubrication and cooling for the bit and to provide a vehicle for removal of drill cuttings from the earth formation being drilled. The erosive character of the drilling fluid medium typically causes wear of both the piston and pump cylinder but the pump cylinder, when worn, can develop a condition that causes rapid deterioration of the piston construction. As the metal pump cylinder becomes worn due to erosion, the annular space between the piston and the cylinder wall will increase substantially. As fluid pressure is applied to the elastomeric sealing portion of the piston, the elastomeric material can be forced or extruded into this annular space. When this occurs, the extruded portion of the elastomeric material is very quickly and easily damaged by the cutting or tearing action that occurs as the extruded portion of the material is moved linearly along the cylinder wall. Any transverse movement of the piston during such linear movement can cause the extruded elastomeric sealing material of the piston to be pinched between the metal portions of the piston and the cylinder wall, thus developing a cutting or pinching action that quickly deteriorates the elastomeric material immediately adjacent the annular metal portion of the piston hub.
When a piston becomes worn due to pinching or accelerated deterioration of the elastomeric material, the annular metal portion of the piston hub structure can contact and cause further accelerated wear of the pump cylinder during use. Under the circumstance where accelerated wear is occuring it is necessary that the mud pump be taken out of service for sufficient period of time that the piston and pump cylinder can be replaced. Obviously, when the mud pump systems of a drilling rig are out of service for repair, unless supplemental or auxiliary mud pumps are provided, it is necessary to discontinue the drilling operation until such time as appropriate repairs are made. In order to facilitate optimum drilling operations, it is of course appropriate that mud pump systems be provided that will function for extended periods of time without requiring replacement of the pistons or cylinders. It is also desirable that a pump piston construction be provided that has a bearing capability that will prevent unnecessary wear of the metal pump cylinder of the mud pump even under high pressure service conditions.
Accordingly, it is a feature of the present invention to provide a novel pump cylinder construction incorporating an elastomeric sealing member and also incorporating an anti-extrusion member that effectively prevents extrusion of the elastomeric sealing material into the annular space between the piston and the pump cylinder.
It is also a feature of the present invention to provide a novel piston construction for reciprocating pumps incorporating an elastomeric sealing member that functions to transmit fluid pressure and cause pressure induced radial expansion of an anti-extrusion member that functions to minimize the annular spacing between the piston construction and the cylinder wall.
Another feature of the present invention contemplates the provision of a novel piston construction for reciprocating pumps wherein an anti-extrusion member is provided that also provides a bearing capability to minimize wear of the pump cylinder during use.
A further feature of the present invention concerns a novel pump piston construction incorporating an annular sealing element composed of elastomeric material and an anti-extrusion member composed of a relatively hard but yieldable plastic material, the outer portion of which is yielded radially outwardly responsive to fluid pressure transmitted through the elastomeric material and bearing upon an internal surface thereof.
It is also a feature of the present invention to provide a novel pump piston construction incorporating an elastomeric sealing member and an annular anti-extrusion member with the sealing member and anti-extrusion member being of mating structurally interrelated construction.
It is an even further feature of the present invention to provide a novel pump piston construction wherein the elastomeric sealing portion of the piston construction is bonded to an anti-extrusion member and the hub structure of the piston, thereby allowing the piston be replaceable as a unit.
It is also a feature of the present invention to provide piston construction wherein an annular elastomeric sealing member and an annular anti-extrusion member composed of heat resistant plastic material are bonded together and the sealing member and anti-extrusion member are also bonded to the hub portion of the piston construction.
It is another feature of this invention to provide a novel pump piston construction incorporating an annular sealing member and an anti-extrusion member that are structurally interlocked with the metal hub portion of the piston.
Other and further objects, advantages and features of the present invention will become apparent to one skilled in the art upon consideration of this entire disclosure. The form of the invention, which will now be described in detail, illustrates the general principles of the invention, but it is to be understood that this detailed description is not to be taken as limiting the scope of the present invention.